1. Field of the Invention
The present invention relates to electronic cameras and, more particularly, to an electronic camera having a built-in strobe suitable for use in an electronic still camera or the like.
2. Description of the Prior Art
Various types of recording apparatus, have previously been developed in the art, including so-called electronic still cameras, each for recording a still picture in the form of an electric image signal on a magnetic disk. In order to perform the photographing operation by using the electronic still camera, its exposure condition is required to be controlled in the same manner as a general still camera using a metal halide film. As the exposure control methods when photographing an object by using a strobe in the night and so forth there are two approaches, one being to control the exposure by controlling an amount of emission light of the strobe and the other being to control the exposure by controlling an opening degree of an iris and a shutter speed while making an amount of the light emission of the strobe constant.
The former method of controlling the exposure by controlling an amount of the light emission of the strobe is called an auto-strobe control method, wherein the amount of the light emission of the strobe is controlled by detecting incident radiation or an amount of light which is reflected from an object to which light is emitted from the strobe. This auto-strobe control method can be realized with relatively simplified constructions and so the method has been applied broadly to various types of cameras with strobes.
The latter method of controlling the exposure by controlling an opening degree of an iris and a shutter speed while making an amount of the light emission of the strobe constant is called a "flashmatic method", wherein the opening degree of an iris and a shutter speed are controlled in accordance with a distance between the camera and an object. Thus, this method requires an accurate control of the opening degree of an iris and a shutter speed in accordance with information of the distance in order to suitably control the exposure, so that this method has not been used generally. In particular, in an electronic still camera, an exposure latitude capable of performing proper photographing is narrower when compared with that of a still camera using a silver film and so it is required to control the exposure value more strictly when compared with a still camera using a silver film. Thus, it has been difficult to apply the flashmatic method to an electronic still camera and so the auto-strobe method has been applied thereto generally.
Now, there is known a type of camera that is capable of photographing an object positioned in a range of distance shorter than the normal range of distance which can be focused by rotating a normal focus ring, that is, a camera capable of performing macroscopic photographing. In this type of camera, the distance between the camera and an object capable of performing the macroscopic photographing is around 50 cm, for example. When performing the macroscopic photographing by using this type of camera, a field angle of a photographing lens or the photographing lenses sometimes does not coincide with an incident angle of a photo receptor element which detects an amount of light reflected from an object to which a light beam is emitted from a strobe due to the distance between the camera and an object. In this case, the auto-strobe control can not be performed satisfactorily, so that the exposure may not performed suitably.
This phenomenon will be explained with reference to FIG. 2 illustrating major portions of a typical example of conventional electronic still cameras. In FIG. 2, an object image is focused on an image plane of a solid state image-pickup element 2 such as a charge-coupled device (CCD) through a photographing lens 1, or a plurality of lenses. The solid state image-pickup element 2 converts the focused image into an electric image signal and applies it to an image signal processing circuit 3 which in turn converts the image signal into a predetermined video signal. The video signal is applied to a recording portion (not shown) through an output terminal 4. In this case, an aperture is determined by controlling an opening degree of an iris 5 disposed in the vicinity of the photographing lens 1 and a shutter speed is determined in accordance with a time period during which the light is received on the image plane of the solid state image-pickup element 2.
A strobe or a stroboscopic lamp 6 is mounted on the camera at a position apart from the photographing lens 1. The light emission of the strobe 6 is controlled by a light emission control circuit 7 in an interlocked relation with the photographing operation. Further, a photo receptor element 8 used in the auto-strobe control for detecting an amount of light reflected from an object to which a light is emitted from the strobe 6 is mounted in the vicinity of the photographing lens 1. The photo receptor element 8 delivers information representing the detected amount of the reflected light from an object to the light emission control circuit 7 when the strobe 6 emits light. The light emission control circuit 7 then controls suitably an amount of emitted light, i.e. a time period during which the strobe 6 emits light, in accordance with the information of the detected amount of the reflected light to thereby perform the auto-strobe operation.
In a normal photographing operation for photographing an object in a normal range where the distance between the photographing lens 1 and an object ml is more than 80 cm, for example, the field angle of the photographing lens 1 coincides with the incident angle of the photo receptor element 8, while in the macroscopic photographing operation where the distance between the photographing lens 1 and an object m2 is about 50 cm, for example, the incident angle of the photo receptor element 8 can not cover all of the field angle of the photographing lens 1 due to a difference of mounted position between the photographing lens 1 and the photo receptor element 8. Thus, in the macroscopic photographing mode, the return light from the object m2 can not be detected satisfactorily on the basis of the light incident on the photo receptor element 8 so that the auto-strobe operation can not be performed satisfactorily and hence the exposure can not be performed suitably.
In order to overcome this drawback in the macroscopic photographing mode, it is proposed to control the exposure by the flashmatic method. However as described above, use of the flashmatic method requires an accurate measurement of the distance between the camera and an object and so forth in order to suitably control the exposure, resulting in complex constructions of the camera.